It is known that, at the rear of a turbojet engine nozzle, the jet emitted by this nozzle comes into contact with at least one other gaseous flow: in the case of a straight-flow turbojet engine, this jet comes into contact with the ambient air whereas, in the case of a bypass turbojet engine, the cold flow and the hot flow come into contact, not only with one another, but also with the ambient air.
Because the speed of the jet emitted by said nozzle differs from the speed of said other gaseous flow or flows encountered by said jet, this results in fluidic shear as said flows interpenetrate, said fluidic shear giving rise to noise, generally known as “jet noise” in aeronautical parlance.
In order to attenuate such jet noise, the idea of generating turbulence at the boundaries between said flows with different speeds has already been put forward.
For example, document GB-A-766 985 describes a nozzle of which the outlet orifice is provided, at its periphery, with a number of projections which extend rearward and the overall direction of which is at least approximately that of the jet emitted by said nozzle. Such projections consist of “teeth” which may exhibit numerous different shapes.
As an alternative, document GB-A-2 289 921 proposes to make notches in the edge of the outlet orifice of the nozzle. Such notches are distributed about the periphery of said outlet orifice and each of them generally has the at least approximate shape of a triangle, the base of which coincides with said edge of the outlet orifice and the vertex of which is situated forward of this outlet edge. This results in the formation, between two consecutive notches, of a tooth in the at least approximate shape of a triangle or trapezoid.
Whatever their precise shape, such teeth are generally known in aeronautical parlance as “chevrons”.
The known chevrons are generally effective at attenuating jet noise but have the disadvantage of giving rise to a significant amount of drag, particularly in cruising flight.
In order to address this disadvantage, it is already known practice (known for example from EP-1 580 419) for the length of the chevrons to be shortened. To do this, the shape of each chevron is delimited:                by two lateral sides of which the front ends are secured to said nozzle and which, with increasing distance therefrom, converge toward one another without meeting so that the rear ends of said lateral sides are separated from one another; and        by a transverse line which connects the rear ends of said lateral sides thereby forming two lateral protrusions separated by an intermediate recess.        
However, in such a known chevron, said lateral protrusions and said intermediate recess form sharp points which behave as additional parasitic noise sources. Hence, whatever is saved in terms of drag is lost in terms of noise.
It is an object of the present invention to reduce the noise emissions of such a known chevron while at the same time enjoying its reduction in drag.